Building the llvm-base package is fragile due to its configuration process.
It would be much simpler, if LLVM would support pkg-config
since this is nicely integrated in Cabal.
However, LLVM developers do not seem to care much about it:
http://llvm.org/bugs/show_bug.cgi?id=9405.
If we are lucky we get pkg-config support in Debian Linux.
Until this comes true, you can use this program.
It calls llvm-config and writes its output to a PC file.